v3.26.1
Investments - Selected Balance Sheet Information for SLP III and SLP IV (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Investments, cost $ 2,464,428 [1] $ 2,912,115 [2]
Investments at fair value 2,289,805 [1] 2,742,013 [2]
Receivable from unsettled securities sold 0 4,138
Total assets 2,415,453 2,902,853
Deferred financing costs, accumulated amortization 48,929 45,302
Deferred financing costs (net of accumulated amortization) (15,416) (17,875)
Payable for unsettled securities purchased 313 463
Other liabilities 2,678 2,181
Total liabilities 1,380,638 1,714,597
Total liabilities and net assets 2,415,453 2,902,853
SLP III    
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Investments, cost 977,200 957,232
Investments at fair value 919,844 941,427
Cash and other assets 35,195 28,469
Receivable from unsettled securities sold 4,577 0
Total assets 959,616 969,896
Deferred financing costs, accumulated amortization 8,557 7,948
Deferred financing costs (net of accumulated amortization) (3,699) (4,308)
Payable for unsettled securities purchased 7,671 105,171
Distribution payable 6,000 7,000
Other liabilities 10,715 8,462
Total liabilities 821,387 789,025
Members' capital 138,229 180,871
Total liabilities and net assets 959,616 969,896
SLP III | Revolving Credit Facility    
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Credit facility 800,700 672,700
SLP IV    
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Investments, cost 663,523 654,867
Investments at fair value 624,995 641,452
Cash and other assets 19,550 31,324
Receivable from unsettled securities sold 2,963 0
Total assets 647,508 672,776
Deferred financing costs, accumulated amortization 4,863 4,022
Deferred financing costs (net of accumulated amortization) (3,603) (4,444)
Payable for unsettled securities purchased 3,385 4,826
Distribution payable 4,290 66,866
Other liabilities 8,372 6,978
Total liabilities 546,581 545,963
Members' capital 100,927 126,813
Total liabilities and net assets 647,508 672,776
SLP IV | Revolving Credit Facility    
Investment Company, Nonconsolidated Subsidiary [Line Items]    
Credit facility $ 534,137 $ 471,737
[1] New Mountain Finance Corporation (the "Company") generally acquires its investments in private transactions exempt from registration under the Securities Act of 1933, as amended (the "Securities Act"). These investments are generally subject to certain limitations on resale, and may be deemed to be "restricted securities" under the Securities Act.
[2] New Mountain Finance Corporation (the "Company") generally acquires its investments in private transactions exempt from registration under the Securities Act of 1933, as amended (the "Securities Act"). These investments are generally subject to certain limitations on resale, and may be deemed to be "restricted securities" under the Securities Act.